Ozone Treatment: A Versatile Tool for the Postsynthesis Modification of Porous Silica-Based Materials

Abstract

Facile synthesis of silica-based functional materials at low temperatures has remained a challenge in materials science. To this end, we demonstrate the use of a gaseous ozone stream, generated via an electric discharge method, as a versatile tool for the postsynthesis modification of silica-based functional nanomaterials. First, a parametric study is conducted with a mesoporous model material to obtain basic insights into the reaction of the organics with ozone. The study is then extended to a number of distinct silica-based inorganic materials. The scope of ozone treatment can be broadly classified into three categories: (a) elimination of templates or structure directing agents (SDAs) from materials with pore sizes ranging from 0.5 to 10 nm, (b) selective transformation of organic groups functionalized on the mesoporous silica, and (c) simultaneous elimination of intermediate polymeric shells and template from the outer shells to obtain yolk−shell type materials. Each material studied here requires different parameters (temperature, time, and concentration of ozone) depending on its physical and chemical properties which have been carefully examined. Overall, the study demonstrates the potential of ozone treatment in tailoring functional materials at low temperature and provides vital insights into the reaction of ozone with silica-based materials. The study shows that gaseous ozone treatment is not limited to only one type of materials but can be applied to many systems, and we are convinced that the methodology can be applied to a multitude of organic@inorganic systems way beyond the scope of materials presented here.

Experimental methods in chemical engineering: specific surface area and pore size distribution measurements—BET, BJH, and DFT

“…DFT is considered a more realistic and adaptable calculation approach of pore size distribution. This is, for instance, evidenced by the results in Table , from the differences between average pore size diameter determined by the BJH and DFT methods for mesoporous silica after template removal, either by air calcination or ozone treatment . For samples OTMS, BJH results are close to DFT ones, while for samples CTAC and SBA‐15 pore diameters estimated by DFT are almost 1 nm and 2 nm higher, respectively.…”

“…The non-local density functional theory (NLDFT) reliably predicts pore sizes of ordered mesoporous molecular sieves (silicas) given suitable parameters for adsorbate-adsorbent interactions. [29][30][31] Physisorption analysis softwares, such as Autosorb-1, solve the set of equations by non-negative least squares. [32] For carbonaceous materials, NLDFT assumes slit-shaped pores without network connections yet with ideal graphitic walls.…”

“…This is, for instance, evidenced by the results in Table 1, from the differences between average pore size diameter determined by the BJH and DFT methods for mesoporous silica after template removal, either by air calcination or ozone treatment. [31] (122). The most prolific science category was physical chemistry with 2015 occurrences.…”

“…The theory relies on a theoretical description of the experimental adsorption isotherm N exp ( P / P 0 ) Equation : where f ( D ) is an unknown pore diameter distribution function; and D m and D M are the minimum and maximum pore sizes in the kernel, respectively. The non‐local density functional theory (NLDFT) reliably predicts pore sizes of ordered mesoporous molecular sieves (silicas) given suitable parameters for adsorbate‐adsorbent interactions . Physisorption analysis softwares, such as Autosorb‐1, solve the set of equations by non‐negative least squares .…”

“…NaCl promoted the formation of a 3D‐Fe/N/C with a much higher SSA and, as a result, higher activity in the electrocatalytic process, owing to the facilitated transfer of O 2 molecules. Joshi et al used two approaches for template removal including air calcination and ozone treatment, and reported that except for octadecyltrimethoxysilane mesoporous silica (OTMS), the former provides pore structures with higher BET surface area (Table ).…”